The invention relates to a volumetric machine gear pump or motor comprising a tubular casing, two end plates closing the axial ends of the casing, two rigid bearings received in the casing adjacent the respective end plates, meshing gearwheels each received between the two bearings, and means for balancing each bearing comprising a chamber defined between the bearing and the adjacent end plate and means for admitting to each chamber a fluid whose pressure increases with the delivery pressure of the pump or inlet pressure of the motor, an internal shoulder being provided on the casing between the bearings to limit the minimum distance between the proximate faces of the bearings to a value greater than the axial length of each gearwheel. The outer periphery of the bearings and recesses in the casing adapted to receive such bearings may be inter alia circular.
In a machine of the kind specified, to obtain a satisfactory performance the axial clearance between the gearwheels and the bearings during operation must be less than a predetermined limit. The limit is as a rule low and the machining accuracy of the various members of which the known volumetric machine is composed do not enable such demands to be systematically met. As a result, the various casings manufactured must be selected and matched with gearwheels whose dimensions are such as to meet the clearance requirement if satisfactory performance is to be achieved.
Moreover the performance of a machine of the kind specified depends considerably on the way in which the bearings supporting the gearwheels are balanced, since any deformation of the bearings, caused inter alia by hydraulic pressures developing during the operation of the machine, is accompanied by leakages which interfere with machine performance.
It is a main object of the invention to adapt a machine of the kind specified in such a way that it meets more satisfactorily the various practical requirements, inter alia so that its manufacture is simplified and its performance improved.